The present invention relates to compounds that are soluble in or miscible in carbon dioxide and to methods of synthesizing such compounds.
Various publications are referenced herein to, for example, clarify the general state of the art. Reference to a publication herein is not an admission that the publication is prior art or relevant to the patentability of the present invention.
The feasibility of using carbon dioxide or CO2 as a process solvent has been extensively investigated in both academic and industrial circles because CO2 is considered to be an environmentally benign solvent. Previous solubility parameter calculations using equation of state information suggested that the solvent power of CO2 was similar to that of short n-alkanes, leading to hopes that CO2 could replace a wide variety of non-polar organic solvents. King, J. W., Poly. Mat. Sci. Eng. Prepr. (1984), 51, 707. Although such solubility parameter values precluded the use of CO2 for processing of polar or hydrophilic materials, it was believed that addition of conventional alkyl-functional surfactants could effectively deal with the problem. However, early attempts to employ conventional surfactants in CO2 failed as a result of the poor solubility of the amphiphiles, despite the fact that these same molecules exhibited adequate solubility in ethane and propane. Consani, K. A.; Smith, R. D.; J. Supercrit. Fl. (1990), 3, 51. It was later discovered that the early solubility parameter calculations, while mathematically correct, failed to note that the absolute value was inflated by as much as 20% by the strong quadropole moment of CO2 (which also inflates its critical pressure). Myers, A. L.; Prausnitz, J. M., Ind. Eng. Chem. Fundam. (1965), 4, 209.
Johnston and colleagues suggested polarizability/volume as a better quantity by which to judge solvent power. O""Shea, K.; Kirmse, K.; Fox, M. A.; Johnston, K. P.; J. Phys. Chem. (1991), 95, 7863 (b) McFann, G. J.; Howdle, S. M.; Johnston, K. P.; AIChE J. (1994), 40, 543 (c) Johnston, K. P.; Lemert, R. M.; in Encyclopedia of Chemical Processing and Design, McKetta, J. J., Ed; Marcel Dekker: New York (1996), 1. On the basis of polarizability/volume, CO2 is a poor solvent compared to short n-alkanes. As the 1980""s drew to a close, a number of research groups began to explore the design of CO2-philic materials, (that is, compounds which dissolve in or are miscible in CO2 at significantly lower pressures than alkyl functional analogs). For example, Harrison et al. generated a hybrid alkyl/fluoroalkyl surfactant that both dissolved in CO2 and solubilized significant amounts of water. Harrison, K.; Goveas, J.; Johnston, K. P.; O""Rear, E. A.; Langmuir (1994), 10, 3536. DeSimone and coworkers generated homo- and copolymers of fluorinated acrylates which exhibit complete miscibility with CO2 at moderate pressures. DeSimone, J. M.; Guan, Z.; Elsbernd, C. S.; Science (1992), 257, 945. Block copolymers featuring fluorinated acrylate monomers were used to support dispersion polymerization in CO2, allowing generation of micron-size monodisperse spheres. Hsiao, Y. L.; Maury, E. E.; DeSimone, J. M.; Mawson, S. M.; Johnston, K. P.; Macromolecules (1995), 28, 8159. Fluoroether-functional amphiphiles have been used to support emulsion polymerization as described in Adamsky, F. A.; Beckman, E. J.; Macromolecules (1994), 27, 312, solubilize proteins as described in (a) Ghenciu, E.; Russell, A. J.; Beckman, E. J.; Biotech. Bioeng (1998), 58, 572 (b) Ghenciu, E.; Beckman, E. J.; Industr. Eng. Chem. Res. (1997), 36, 5366; and Johnston, K. P.; Harrison, K. L.; Clarke, M. J.; Howdle, S.; Heitz, M. P.; Bright, F. V.; Carlier, C. Randolph, T. W.; Science (1996), 271, 624, and extract heavy metals from soil and water as described in (Yazdi, A. V.; Beckman, E. J.; Ind. Eng. Chem. (1997), 36, 2368; and Li, J.; Beckman, E. J.; Industr. Eng. Chem. Res. (1998), 37, 4768.
In general, compounds not soluble or miscible in CO2 (that is, CO2-phobic compounds) can be made soluble or miscible in CO2 by synthesizing analogs of such compounds incorporating one or more CO2-philic groups. Processes and reactions that are normally not possible in CO2, are thereby made possible. For example, surfactants, chelating agents and reactants for use in carbon dioxide can be synthesized in this manner. CO2-phobic compounds that can be modified with CO2-philic groups to create CO2-philic analogs for processing in CO2 are disclosed, for example, in U.S. patent application Ser. No. 09/106,480, entitled Synthesis of Hydrogen Peroxide and filed Jun. 29, 1998, the disclosure of which is incorporated herein by reference, in which hydrogen peroxide is synthesized in CO2 using a CO2-philic functionalized anthraquinone reactant. Moreover, CO2-philic chelating agents for extraction of metals in carbon dioxide are disclosed U.S. Pat. No. 5,641,887 and U.S. Pat. No. 5,872,257, the disclosures of which are incorporated herein by reference. Other CO2-philic functionalized compounds are disclosed in U.S. Pat. No. 5,589.105, U.S. Pat. No. 5,789,505, U.S. Pat. No. 5,639,836, U.S. Pat. No. 5,679,737, U.S. Pat. No. 5,733,964, U.S. Pat. No. 5,780,553, U.S. Pat. No. 5,858,022, U.S. Pat. No. 5,676,705, U.S. Pat. No. 5,683,977, and U.S. Pat. No. 5,683,473, the disclosures of which are incorporated herein by reference.
It has been theorized that only molecules with very low solubility parameters (that is, fluorine-containing and silicon-containing molecules) are sufficiently CO2-philic to synthesize CO2-philic analogs or amphiphiles suitable for commercial processing in CO2. O""Neill, M. L., Cao, Q.; Fang, M.; Johnston, K. P.; Wilkinson, S. P.; Smith, C. D.; Kerschner, J. L.; Jureller, S. H.; Ind. Eng. Chem. Res. (1998), 37, 3067. Indeed, it is the common belief in the art that only fluorine-containing and silicon-containing molecules are viable solutions in synthesizing commercially viable CO2-philic analogs. The most successful CO2-philic modifiers or moieties to date are fluorinated compounds. Despite success in development of fluorinated and silicon-containing CO2-philic amphiphiles, the cost (on a mass basis) of these materials (typically, on the order of $1/gram) renders the economics of a process unfavorable unless the amphiphile can be efficiently recycled. Whereas in-process recycling of a xe2x80x9cCO2-philexe2x80x9d may at times be straightforward, this is not true in all cases where CO2 has been proposed as a replacement for organic solvents.
It is very desirable to develop CO2-philic compounds or CO2-philes that are effectively soluble in or miscible in CO2 while being relatively inexpensive to synthesize and use.
The present invention provides, generally, a method of synthesizing a CO2-philic analog of a CO2-phobic compound, comprising the step of: reacting the CO2-phobic compound with a CO2-philic compound to create the CO2-philic analog. Preferably, the CO2-philic compound contains no F or Si.
Preferably, the CO2-philic compound is a polyether substituted with at least one side group including a group that interacts favorably with or has an affinity for CO2 (preferably a Lewis base group), a poly(ether-carbonate), a poly(ether-carbonate) substituted with at least one side group including preferably a Lewis base, a vinyl polymer substituted with at least one side group including preferably a Lewis base, a poly(ether-ester) or a poly(ether-ester) substituted with at least one side group including preferably a Lewis base. Preferably, the CO2-philic compound contains no F or Si atoms. The CO2-philic analog of the CO2-phobic compound has increased solubility or miscibility in CO2 (that is, increased CO2-philic nature) compared to the CO2-phobic compound.
In one embodiment, the CO2-philic compound is a polyether copolymer including the repeat units 
wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 are, independently, the same or different, H, an alkyl group, xe2x80x94(R22xe2x80x2)R22, or R4 and R6 form of carbon cyclic chain of 3 to 8 carbon atoms. R22xe2x80x2 is a spacer or connecting group, and preferably is an alkylene group, and z is 0 or 1. R22 is a group that interacts favorably with CO2 and is preferably a Lewis base group. Preferably, at least one of R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 is xe2x80x94(R22xe2x80x2)zR22.
In the above equation, i, j, k, l, m, and n are independently, the same or different, 0, 1 or 2. At least one of i, j, and k is 1 or 2, and at least one of l, m, and is 1 or 2. x and y are integers. Preferably, i, j, k, l, m, and n are 0 or 1. More preferably, i is 0, j is 1, k is 1, l is 0, m is 1 and n is 1. In the case that one of i, j, k, l, m, or n is 2, each of the substituents on the two carbon atoms can be different. In that regard, for example, xe2x80x94(CR1R2)2xe2x80x94 expands to xe2x80x94(CR1R2-CR1xe2x80x2R2xe2x80x2)xe2x80x94 wherein R1, R2, R1xe2x80x2, and R2xe2x80x2 are, independently, the same or different, H, an alkyl group, xe2x80x94(R22xe2x80x2)zR22. Likewise, pendant R""s on adjacent carbons can form a carbon chain of 3 to 8 carbon atoms.
In several embodiments R22xe2x80x2 is xe2x80x94(CH2)axe2x80x94 and a is an integer between 0 and 5. Preferably, a is 1 or 2. Suitable Lewis base groups R22, include, but are not limited to, carbonyl-containing groups such as xe2x80x94Oxe2x80x94C(O)xe2x80x94R23 or xe2x80x94C(O)xe2x80x94R23, xe2x80x94Oxe2x80x94P(O)xe2x80x94(Oxe2x80x94R23)2, or xe2x80x94NR23R23xe2x80x2, wherein R23 and R23xe2x80x2 are preferably independently, the same or different, an alkyl group.
In one embodiment in which i is 0, j is 1, k is 1, l is 0, m is 1 and n is 1, R3, R4, R5, R9, R10, and R11 are H, R6 is an alkyl group and R12 is a Lewis base. For example, the lewis base group can be Oxe2x80x94C(O)xe2x80x94R23. In one such embodiment, R23 is a methyl group. In one embodiment the methyl group is substituted with a Cl (xe2x80x94CH2Cl).
Preferably, the polyether copolymer contains no F or Si atoms.
In the repeat units of the polyether, x and y are integers. Preferably x and y are each at least 1. Preferably, the total chain length of the CO2-philic group (x+y) is less than approximately 400 repeat units. More preferably, the total chain length of the CO2-philic group (x+y) is less than approximately 200 repeat units. For many application (for example, surfactants) the total chain length is preferably between 5 and 50 repeat units. More preferably, the chain length in such applications is between approximately 20 to 40 repeat units. The percentage of repeat units including a Lewis base group is preferably in the range of approximately 1 to approximately 50%. More preferably, the percentage of repeat units including a Lewis base group is in the range of approximately 5 to approximately 35%. Even more preferably, the percentage of repeat units including a Lewis base group is in the range of approximately 10 to approximately 25%.
In another embodiment, the CO2-philic compound is a poly(ether-carbonate) copolymer including the repeat units: 
wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 are, independently, the same or different, H, an alkyl group, xe2x80x94(R22xe2x80x2)zR22, or R4 and R6 form of carbon cyclic chain of 3 to 8 carbon atoms as described above. Likewise, i, j, k, l, m and n are as described above (0, 1 or 2). Preferably, i, j, k, l, m and n are 0 or 1. In several embodiments, i and l are 0, and j, k, m and n are 1. In this copolymer a Lewis base group is incorporated into the copolymer backbone. The copolymer can also include one or more pendant groups that react favorably with CO2 (preferably, Lewis base groups). Preferably, the poly(ether-carbonate) copolymer contains no F or Si atoms.
In one embodiment i and l are 0, j, k, m and n are 1, R3, R4, R5, R9, R10, and R11 are H, R6 is an alkyl group (for example, a methyl group) and R12 is an alkyl group (for example, a methyl group).
In the repeat units of the polycarbonate, xxe2x80x2 and yxe2x80x2 are integers and, preferably, each is at least 1. Preferably, the total chain length of the CO2-philic group (xxe2x80x2+yxe2x80x2) is less than approximately 400 repeat units. More preferably, the total chain length of the CO2-philic group is less than approximately 200 repeat units. For many application (for example, surfactants) the total chain length is preferably between 5 and 50 repeat units. More preferably, the chain length in such applications is between approximately 20 to 40 repeat units. The percentage of repeat units including the carbonate linkage (that is, the Lewis base in the copolymer backbone indicated by yxe2x80x2) is preferably in the range of approximately 1 to approximately 50%. More preferably, the percentage of repeat units including the carbonate linkage is in the range of approximately 5 to approximately 35%. Even more preferably, the percentage of repeat units including the carbonate linkage is in the range of approximately 10 to approximately 25%.
In one aspect, the vinyl polymer is a copolymer including the repeat units: 
wherein R13, R14, R15, R16, R17, R18, R19, and R20 are, independently, the same or different, H, an alkyl group, an alkenyl group, xe2x80x94Oxe2x80x94R24, xe2x80x94(R22xe2x80x2)zR22, wherein, z, R22xe2x80x2 and R22 are as described above. Preferably, at least one of R13, R14 R15, R16, R17, R18, R19, and R20 is xe2x80x94(R22xe2x80x2)zR22. xxe2x80x3 and yxe2x80x3 are integers. The vinyl copolymer preferably contains no F or Si atoms.
In several embodiment, R22xe2x80x2 is xe2x80x94(CH2)axe2x80x94 and a is an integer between 0 and 5. In such embodiments, a is preferably 1 or 2 and R22 is, for example, xe2x80x94Oxe2x80x94C(O)xe2x80x94R23, xe2x80x94C(O)xe2x80x94R23, xe2x80x94Oxe2x80x94P(O)xe2x80x94(Oxe2x80x94R23)2, or xe2x80x94NR23R23xe2x80x2, wherein R23 and R23, are independently, the same or different, an alkyl group.
In the polyvinyl copolymer, xxe2x80x3 and yxe2x80x3 are integers and preferably each is at least 1. Preferably, the total chain length of the CO2-philic group (xxe2x80x3+yxe2x80x3) is less than approximately 400 repeat units. More preferably, the total chain length of the CO2-philic group is less than approximately 200 repeat units. For many application (for example, surfactants) the total chain length is preferably between 5 and 50 repeat units. More preferably, the chain length in such applications is between approximately 20 to 40 repeat units. The percentage of repeat units including a Lewis base is preferably in the range of approximately 1 to approximately 50%. More preferably, the percentage of repeat units including a Lewis base is in the range of approximately 5 to approximately 35%. Even more preferably, the percentage of repeat units including a Lewis base is in the range of approximately 10 to approximately 25%.
In another aspect, the CO2-philic compound is a poly(ether-ester) copolymer including the repeat units 
wherein R1, R2, R3, R4, R5 and R6 are as defined above, and i, j and k are as defined above (0, 1 or 2). Preferably, i, j, k, l, m and n are 0 or 1. In several embodiments, i and l are 0, and j, k, m and n are 1. R21 is a connecting group that can, for example, be an alkylene group (a difunctional alkyl group), a cycloalkylene group (a difunctional cycloalkyl group), a difunctional ester group, (for example, xe2x80x94(CR25R26)pxe2x80x2, xe2x80x94(CR27R28)pxe2x80x3xe2x80x94), a difunctional ether group (for example, xe2x80x94(CR25R26)pxe2x80x2, xe2x80x94Oxe2x80x94(CR27R28)pxe2x80x2. R25, R26, R27 and R28 are preferably independently H or an alkyl group. xxe2x80x2xe2x80x3 and yxe2x80x2xe2x80x3 are integers.
Such poly(ether ester) copolymers include a Lewis base group in the copolymer backbone. The copolymer can also include one or more pendant groups that interact favorably with CO2 (preferably, Lewis base groups). In that reagard, at least one of R1, R2, R3, R4, R5 and R6 can be xe2x80x94(R22xe2x80x2)zR22, wherein R22xe2x80x2 and R22 are as defined above. The group R22 can, for example, be Oxe2x80x94C(O)xe2x80x94R23, xe2x80x94C(O)xe2x80x94R23, xe2x80x94Oxe2x80x94P (O)xe2x80x94(Oxe2x80x94R23)2, or xe2x80x94NR23R23xe2x80x2, wherein R23 and R23xe2x80x2 are as defined above.
In a number of embodiments, R22xe2x80x2 is xe2x80x94(CH2)axe2x80x94 and a is an integer between 0 and 5. In several such embodiments, a is 1 or 2 and i is 0, j is 1, and k is 1.
In the polyvinyl copolymer, xxe2x80x2xe2x80x3 and yxe2x80x2xe2x80x3 are integers and preferably each is at least 1. Preferably, the total chain length of the CO2-philic group (xxe2x80x2xe2x80x3+yxe2x80x2xe2x80x3) is less than approximately 400 repeat units. More preferably, the total chain length of the CO2-philic group is less than approximately 200 repeat units. For many application (for example, surfactants) the total chain length is preferably between 5 and 50 repeat units. More preferably, the chain length in such applications is between approximately 20 to 40 repeat units. The percentage of repeat units including the ester linkage (that is, the Lewis base in the copolymer backbone indicated by yxe2x80x2xe2x80x3) is preferably in the range of approximately 1 to approximately 50%. More preferably, the percentage of repeat units including the carbonate linkage is in the range of approximately 5 to approximately 35%. Even more preferably, the percentage of repeat units including the carbonate linkage is in the range of approximately 10 to approximately 25%.
The polyether copolymers, poly(ether-carbonate) copolymers, vinyl copolymers and poly(ether-ester copolymers) described above are preferably not alternating copolymers. Moreover, other monomer or repeat units can incorporated in the copolymers (for example, between the repeat units set forth above).
The present invention also provides a surfactant for use in carbon dioxide, the surfactant includes a CO2-phobic group covalently linked to a CO2-philic segment, wherein the CO2-philic segment includes a polyether substituted with at least one side group including a group that interacts favorably with CO2 (preferably a Lewis base group), a poly(ether-carbonate), a poly(ether-carbonate) substituted with at least one side group including preferably a Lewis base, a vinyl polymer substituted with at least one side group including preferably a Lewis base, a poly(ether-ester) or a poly(ether-ester) substituted with at least one side group including preferably a Lewis base. The polyether, polycarbonate, vinyl polymer and poly(ether-ester) are preferably copolymers as described above.
The CO2-phobic group of the surfactants of the present invention can be generally any head group usable in surfactants, including, but not limited to, H, a carboxylic acid group, a hydroxy group, a phosphate group, a phosphate ester group, a sulfonyl group, a sulfonate group, a sulfate group, a branched or straight chained polyalkylene oxide group, an amine oxide group, an alkenyl group, a nitryl group, a glyceryl group, an aryl group unsubstituted or substituted with an alkyl group or an alkenyl group, a carbohydrate unsubstituted or substituted with an alkyl group or an alkenyl group, an alkyl ammonium group, or an ammonium group. Carbohydrates groups include, for example sugars such as sorbitol, sucrose, or glucose. The CO2-phobic group may likewise include an ion selected from the group of H+, Na+2, Li+, K+, NH4+, Ca+2, Mg+2, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, mesylate and tosylate.
The present invention also provides a chelating agent for use in carbon dioxide. The chelating agent includes a CO2-phobic chelating group covalently linked to a CO2-philic segment, wherein the CO2-philic segment includes a polyether substituted with at least one side group including a group that interacts favorably with CO2 (preferably a Lewis base), a polycarbonate, a polycarbonate substituted with at least one side group including preferably a Lewis base, a vinyl polymer substituted with at least one side group including preferably a Lewis base a poly(ether-ester) or a poly(ether-ester) substituted with at least one side group including preferably a Lewis base. The polyether, polycarbonate, vinyl polymer and poly(ether-ester) are preferably copolymers as described above. The chelating group may, for example, be a polyaminocarboxillic acid group, a thoicarbamate group, a dithoicarbamate group, a thiol group, a dithiol group, a picolyl amine group, a bis(picolyl amine) group or a phosphate group.
The present invention also provides a method of synthesizing a CO2-phile including the step of copolymerizing at least two monomers, wherein a polymer formed from homopolymerization of one of the monomers has a Tg of less than approximately 250 K and a steric factor less than approximately 1.8. At least one of the monomers results in a group in the copolymer that interacts favorably with CO2 (for example, a Lewis base group), and the resultant CO2-phile does not contain both hydrogen bond donors and acceptors. For example, a first monomer can be selected wherein a polymer formed from homopolymerization of the first monomers has a Tg of less than approximately 250 K and a steric factor less than approximately 1.8, while a second monomer results in a repeat unit within the copolymer 15 that includes a Lewis base group (either in the copolymer backbone or pendant therefrom).
The CO2-phile is preferably a polyether, a polycarbonate, a vinyl copolymer or a poly(ether-ester) as described above. A Lewis base group, when pendant, is preferably separated from the CO2-phile backbone by 0 to 5 atoms (more preferably, 1 to 2 atoms).
The present invention also provides a method of synthesizing a CO2-phile comprising the step of copolymerizing carbon dioxide and at least one oxirane. The oxirane may, for example, be epichlorohydrin, ethylene oxide, propylene oxide or cyclohexene oxide.
Prior to the present invention, only fluorous and silicon polymers were thought to be generally suitable for use in creating CO2-philic analogs of CO2-phobic compounds. However, the hydrocarbon CO2-philic compounds and groups of the present invention exhibit phase boundaries in CO2 that occur at pressures comparable to those of fluorinated polyethers of similar chain length, and substantially lower than those of silicones. Moreover, these hydrocarbon CO2-philic groups are substantially less expensive to manufacture and use than fluorinated or silicon compounds.
The CO2-philic compounds and groups of the present invention can be used in a wide variety of applications including, for example, the cleaning industry in which they can be incorporated into surfactants, detergents, fabric softeners and antistatic agents. As chelating agents, they can be used, for example, in metal recovery. The CO2-philic compounds and groups of the present invention can also be incorporated in cleaners used in the electronics industry to, for example, remove oils, greases and other residues from electronic components. The CO2-philic compounds can further be used in dispersants for polymers or inorganic particles (stabilizers), affinity ligands for proteins, catalyst ligands and coatings.